The vertebrate immune response is comprised of multiple molecular and cellular components that must interface to provide the host species with an adequate defense against pathogens. Although much information is available on how individual molecules or cells respond to infection, a complete understanding of the whole-organism response to pathogen exposure remains unresolved, due to the dynamic complexity of the immune system and its interdependent innate and adaptive functionality. The zebrafish larva provides a unique model for overcoming this obstacle as the larva successfully defends itself from pathogens while lacking a functional adaptive immune system for the first 4-6 weeks of life, making it possible to examine exclusively the innate immune response in a whole-organism context. In preliminary transcriptional profiling studies it was found that novel genes that respond to pathogen associated molecular patterns in the zebrafish larva, also respond to infection stimuli in adult zebrafish and mice, underscoring the utility of this novel innate immune model for gene discovery. It is hypothesized that the transcriptional response of zebrafish larvae to infection stimuli will reveal novel genes that mediate innate immunity in mammals. In order to test this hypothesis, two Aims will be achieved, 1) a novel zebrafish larvae assay will be employed to determine the whole-organism transcriptional response to pathogen stimuli in the absence of adaptive immunity, and 2) the role of functionally uncharacterized pathogen-responsive genes will be validated in zebrafish and mammalian innate immune response. The long range goal of the proposed research is to develop an integrative model of innate immune response in the context of the whole organism, on multiple scales, from the individual gene to the transcriptome. Successful completion of the proposed experiments will facilitate novel future investigations, including in vivo visualization of infection response in the transparent zebrafish larva, whole-organism based chemical genetic and mutagenesis screens to identify pharmacological and genetic modifiers of immune response, and gene knock-out/knock- down studies for assessing the role of these immune response genes in immune defense and recovery in both zebrafish and mammals. These data, reagents and tools will constitute a novel systems-based, multi- organism paradigm for investigating, evaluating and modulating the vertebrate innate immune response. PUBLIC HEALTH RELEVANCE The complete, dynamic process by which a vertebrate responds to infection on the organismal level is not well understood. The proposed research will utilize a novel strategy to characterize the genomic response of zebrafish to immune stimuli and use this information to identify uncharacterized mammalian genes that respond to pathogen exposure. The data generated by these methods will provide unprecedented insight into the organism based genomic response to infection, facilitating novel diagnosis, treatment and drug discovery strategies for modulating immune response.